In today's radio communications networks a number of different technologies are used, such as Long Term Evolution (LTE), LTE-Advanced, 3rd Generation Partnership Project (3GPP) Wideband Code Division Multiple Access (WCDMA), Global System for Mobile Communications (GSM), Enhanced Data rate for GSM Evolution (EDGE), Worldwide Interoperability for Microwave Access (WiMAX), and Ultra Mobile Broadband (UMB) to mention a few. A radio communications network comprises radio network nodes providing radio coverage over at least one respective geographical area forming a cell. The cell definition may also incorporate frequency bands used for transmissions, which means that two different cells may cover the same geographical area but using different frequency bands. User equipments (UEs) are served in the cells by the respective radio network node and communicate with the respective radio network node. The UEs transmit data over an air or radio interface to the radio network nodes in uplink (UL) transmissions and the radio network nodes transmit data over an air or radio interface to the UEs in downlink (DL) transmissions.
Traditional radio communications networks broadcast cell-specific reference signals and system information. These signals let UEs determine which cell the UE should connect to and provide information to the UEs as to how they should access those cells.
In particular, the broadcasted system information may comprise parameters that control one or more of the timing, frequency, transmission formats and power to be used by UEs for initial (e.g. random access) transmissions to the network. Such information may be different in different cells, e.g., to be able to distinguish between accesses made in different cells, and/or to adjust the initial UE transmission power levels so as to fit the characteristics of different cells.
Since the wireless communication network (i.e., the radio network node) may not know the location or presence of all UEs in its cell(s), these cell-specific signals are generally broadcasted with constant and relatively high power and high periodicity. This ensures that all UEs will be able to receive such signals at all times.
Future wireless networks (e.g. such as those meeting or expected to meet the criteria for 5G) are expected to support vastly greater numbers of wireless devices, with different classes of devices having very different requirements. For example, numbers of smartphones are likely to increase, with each phone likely to require increasingly high data rates. Conversely, machine-type communication (MTC) devices, such as sensors, meters and the like, may be deployed in even higher numbers, but with much lower requirements for latency and data rate.
Further, future networks are expected to make use of higher frequency bands (e.g. above 60 GHz) where attenuation of the signal with distance is greater. Further still, certain scenarios exist with extreme area coverage requirements; in less densely populated parts of the world (e.g. parts of Australia), a single cell may be required to provide coverage over a much greater area than more densely populated areas.
Using a conventional system information broadcast to reach all such UEs (e.g. smartphones and MTC devices, etc) would be expensive (i.e. in terms of time slots, frequency, transmit power etc). A better solution is required in which resources can be allocated for the transmission of system information more efficiently.
WO 2013/077783 discloses a method in which a system information signature is transmitted or broadcasted by a radio network node of a radio communications network to a UE. The system information signature may comprise an index that indicates which set of system information is to be used by the UE to access the radio communications network. Upon receipt of the system information signature, the UE retrieves system information associated with the signature, and uses that system information to access the network.